Acute bovine footrot, also known as interdigital phlegmon or acute interdigital phlegmon (AIP), is a common infection in cattle [1,11]. The actual prevalence of this disease in many types of cattle is not fully described; however, in some years the prevalence in feedlot animals can reach 10-25% if preventative measures such as feeding antibiotics are not widely implemented.
It is an anaerobic bacterial infection characterized by acute inflammation which is manifested as tissue edema and local infiltration of subcutaneous tissues with polymorphonuclear granulocytic neutrophils (PMN) [16]. Typically this disease involves necrosis of the interdigital epidermis and the underlying dermis. Very often there is an ascending cellulitis which can result in severe swelling from the coronet to the fetlock joint. This infection, if left untreated, can result in sequelae such as septic joint involvement which can lead to euthanasia [2].
The infection is thought to be caused by a synergistic association of anaerobic bacteria including Bacteroides melaninogenicus, Fusobacterium necrophorum [12], and possibly other bacteria such as Dichelobacter (Bacteroides) nodosus [13] or Actinomyces pyogenes [14]. Recently B. melaninogenicus has been divided into several distinct species of bacteria including Porphyromonas sp and Prevotella sp [4]. Fusobacterium necrophorum and B. melaninogenicus have been previously used together to experimentally infect cattle [12]. That investigation did not examine microscopic pathology or the minimum inhibitory concentrations [MIC's] and minimum bactericidal concentrations [MBC's] of the antibiotic(s) for the pathogens used in the experimental infection.
Several treatments have been advocated for acute bovine footrot including IS penicillin [11], oxytetracycline [15], cephalosporins [16], and sulfonamides [11].
Parenteral antibiotic treatment of individual clinically affected animals is effective for treating cattle that can be easily handled and frequently observed. Therapy in fat cattle (i.e., animals nearly ready for marketing as beef) is complicated by the fact that many of these drugs cannot be used without delaying slaughter. Antibiotics without withdrawal periods are available for these animals; however, the expense remains significant. Currently, recommended therapy for these animals can involve daily treatment for up to five days or longer. Cephalosporin, a .beta.-lactam antibiotic, is one recommended therapeutic regimen. For a 500 kg steer, cephalosporin therapy for five days can approach $50 in antibiotic cost alone for a single episode of the disease. This clearly does not include the costs of manpower for giving the treatments, the costs of lost production (e.g., reduced weight gain) in affected cattle, or the significant animal suffering that occurs as a result of this infectious lameness.
There are potentially devastating effects of this disease in breeding bulls if the infection occurs during breeding season and libido is reduced. Conventional antibiotic therapy in mature breeding bulls is problematic because of the frequency of treatments and the massive volume of antibiotic required, in addition to the cost of antibiotics. Although infection can be minimized in some types of cattle through feeding antibiotics, fat cattle are again at high risk because of our inability to use these drugs due to withdrawal times. Preventative measures, such as footbaths, are recommended in many parts of the world but are not practical under many circumstances. The potential environmental implications of using compounds such as blue stone and formaldehyde are also a consideration.
Animals affected with AIP are believed to develop immunity, but the importance of this immunity is unclear [2]. In many acute infectious inflammatory diseases phagocytosis by polymorphonuclear granulocytic neutrophils (PMN) is a central mechanism in the resolution of infection, but these cells have never been specifically evaluated in the context of acute bovine footrot. Specific immunity to etiologic agents of footrot also may be important in resolution of the infection [2]; however, studies have yet to be conducted on precisely how these cells are involved in the mechanisms of this process.
The development of a therapeutic agent and/or a vaccine, additional tools for cattlemen to minimize the effects of footrot, would be worthwhile and a significant contribution to sustainable agricultural practices.
Traditionally, Fusobacterium necrophorum has been described as the cause of bovine footrot [24]. Vaccines based on this microorganism are known and/or available [5,8,9], but efficacy is questionable and use is not broad. Use of 6-substituted 3-nitroimidazo[1,2,b]pyridazine for the control of footrot and liver lesions caused by Fusobacterium necrophorum has also been disclosed [10].